High hydrostatic pressure electrochemical cell

ABSTRACT

THE PRESENT INVENTION RELATES TO NOVEL AND IMPROVED APPARATUS FOR EVALUATING THE ELECTROCHEMICAL AND DIFFUSION PARAMETERS OF HYDROGEN THROUGH A METALLIC SPECIMEN. THE IMPROVED APPARATUS CONTEMPLATES USE OF A HYDROGEN PERMEATION CELL THAT IS SUBDIVIDED INTO A PAIR OF ELECTROLYTIC CELLS BY THE METALLIC SPECIMEN ITSELF. IN ONE ELECTROLYTIC CELL, ONE SURFACE OF THE SPECIMEN IS USED AS A CATHODE ON WHICH A CONTROLLED SUPPLY OF HYDROGEN IS EVOLVED. IN THE OTHER ELECTRLYTIC CELL, THE OTHER SURFACE OF THE SPECIMEN IS USED AS AN ANODE ON WHICH HYDROXYL IONS ARE PRESENT FOR COMBINATION WITH HYDROGEN THAT PERMEATES THE SPECIMEN. LOAD CURRENT IN THE ANODIC CELL INDICATES THE PERMEATION RATE OF HYDROGEN THROUGH THE SPECIMEN. THIS PROCESS IS PERFORMED IN A CONTROLLED TEMPERATURE AND HYDROSTATIC PRESSURE ENVIRONMENT WHICH IS TRANSMITTED TO THE PERMEATION CELL THROUGH A TIMPANIC MEMBRANE IN THE STRUCTURAL WALL OF EACH COMPONENT ELECTROLYTIC CELL.

June 22, 1971 DELUCCIA 3,586,617

HIGH HYDROSTATIC PRESSURE ELECTROCHEMICAL CELL Filed Aug. 26, 1968 2 Sheets-Sheet 1 Fig 1 %L .JWw

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JOHN J. DeLUCClA MLMV 7 ATTORNEY United States Patent 3,586,617 HIGH HYDROSTATIC PRESSURE ELECTROCHEMICAL CELL John J. De Luccia, Springfield, Pa., assignor to the United States of America as represented by the Secretary of the Navy Filed Aug. 26, 1968, Ser. No. 755,354 Int. Cl. B01k 3/00 US. Cl. 204-195 4 Claims ABSTRACT OF THE DISCLOSURE The presentinvention relates to novel and improved apparatus for evaluating the electrochemical and diffusion parameters of hydrogen through a metallic specimen. The improved apparatus contemplates use of a hydrogen permeation cell that is subdivided into a pair of electrolytic cells by the metallic specimen itself. In one electrolytic cell, one surface of the specimen is used as a cathode on which a controlled supply of hydrogen is evolved. In the other electrolytic cell, the other surface of the specimen is used as an anode on which hydroxyl ions are present for combination with hydrogen that permeates the specimen. Load current in the anodic cell indicates the permeation rate of hydrogen through the specimen. This process is performed in a controlled temperature and hydrostatic pressure environment which is transmitted to the permeation cell through a timpanic membrane in the structural wall of each component electrolytic cell.

Hydrogen atoms electrochemically produced as a result of partial or total cathodic reaction on the surface of iron or steel as in the case of corrosion combine to form hydrogen gas or enter the metallic lattice interstitially and permeate through the metal. The presence of hydrogen in the metal can then cause a catastrophic structural failure. It has been shown heretofore that the degree of hydrogen embrittlement in metals is a function of the rate of hydrogen entry into the bulk lattice.

It is therefore a principal object of the invention to provide novel and improved apparatus for determining the rate of permeation of hydrogen through a metallic surface during a cathodic electrolytic process while under hydrostatic pressure.

It is a further object of the invention to provide novel and improved apparatus for determining the effect of change in ambient temperature and pressure on the electrochemical cathodic process.

It is a further object of the invention to provide novel and improved apparatus for simulating deep ocean pressure and temperature environments and determining their effect on the hydrogen embrittlement phenomenon.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 is a diagrammatic view of a preferred embodiment of the present invention;

FIG. 2 is a cross sectional view of the permeation cell shown in FIG. 1; and

FIG. 3 is a diagrammatic view of the permeation cell and its interconnected external circuitry.

Referring now to the various figures of the drawing, it will be noted that the metallic specimen 3, which is to be evaluated, is positioned between the complementary sections 5 and 7 of the Teflon specimen holding device 9. Suitable neoprene 0 rings 11 between the specimen 3 and the upper and lower sections of the holding device 9, as well as juxtaposed interfaces 13 of sections 5 and 7,

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prevent seepage or loss of electrolyte from the cells or onto unexposed portions of the specimen 3. The upper surface of section 7 of the specimen holding device 9 is contoured so as to hermetically engage the lower surface of the U-shaped cathodic cell structure 15 which is filled with a suitable electrolytic solution of .1 normal sulfuric acid and .001 normal hydrochloric acid. Similarly, the lower surface of section 5 of the holding device 9 is contoured so as to hermetically engage the complementary upper surface of the inverted U-shaped anodic cell structure 17 which is filled with a suitable electrolytic solution of .2 normal sodium hydroxide and .01 normal sodium chloride. Timpanic membranes 19 and 21 extend across the open ends of the electrolytic cells 5 and 7 and provide an effective hermetic seal for the electrolytic solutions. The membranes 19 and 21 are secured in position by the holddown rings 23 and 24, 0 rings 25 and 27, and the plastic cell end caps 29 and 31. Elongated bolts 33 that extend through slots in the outer flanged edges of the end caps 29 and 31 hermetically secure various contiguous sections of the permeation cell one to the other.

The platinum or platinum plated anode 35 extends into the interior of the cathodic cell 37 through the plug 39 which is threadedly secured in port 41 in the cell wall. 0 ring 43 hermetically seals the plug 39 in the cell. The silver-silver chloride reference anode 45 also extends into the interior of cell 37 through the plug 47 which is threaded into port 49 in the cell wall. 0 ring 51 provides the necessary hermetic seal. The Pyrex glass capillary tube '53 which surrounds reference electrode 45 localizes electrolytic action in the reference electrolytic circuit to a prescribed area on the specimen 3. In this way, a more reliable reading of its potential on an external recording voltmeter is assured. Similarly, the platinum or platinum plated cathode 55 extends into the interior of the anodic cell 57 through the plug 59 which is threaded into port 61 in the cell. 0 ring 63 hermetically seals the plug 59 in the cell. The silver-silver chloride reference cathode 65 also extends into the interior of the cell 57 through the plug 67 which is threadedly secured in port 69 in the cell wall. 0 ring 71 hermetically seals the plug 67 in the cell. The Pyrex glass cappilary tube 73 which surrounds reference electrode 65 localizes electrolytic action in the reference electrolytic circuit to a prescribed area on the specimen surface. In this way, a more reliable reading of its potential in external circuitry is assured. Make electrical connectors 75 extend outwardly from plugs 39, 47, 59 and 67 and, as will be more apparent hereinafter, provide electrical interconnection of the various anodes of the cell with external electrical circuitry.

Electrical connection of the metallic specimen 3 to circuitry external of the permeation cell is effected by the metallic screw 77 which is threaded into one end of the vertical brass post 79, by the horizontal brass screw 81 that is threaded into the other end of the post 79 and by the needle end of the male electrical connector 83 that is threaded into the projecting portion '85 of section 5 of the specimen holding device 9. 0 rings 87 and 89 protect the electrical connection from the external hydrostatic environment.

The permeation cell 4 is suspended in the hydrostatic pressure vessel 91 in any suitable conventional manner. The Monel head 93 is removably secured in the open end of the pressure vessel 91 by the integral retaining ring 95. Conductors '97, 99, 101, 103 and 105 with suitable associated high pressure insulated female end connectors snap over corresponding male connectors connected to the specimen and the various anodes of the cell 4 and pass through the head of the pressure vessel 91 to external circuitry 107. Thus, as will be more apparent hereinafter, the

recording digital voltmeter 109 is connected across conductors 97 and 99 so as to provide a continuous reading of the electrical potential of the spacimen 3 in the cathodic cell 37. The electrical energy source 111, the variable resistor 113 and the ammeter 115 are series connected across conductors 97 and 101 to provide a variable electrical energy supply source for the cathodic cell 37. The potentiostat 117 and the resistor 119 are connected in the manner shown to conductors 97, 103 and 105 and complete the circuits for the anodic cell 57 and its reference electrode 65. The amplifying electrometer 121 and the anode current recorder 123 are electrically coupled across resistor 119.

Water from the reservoir 125 is pressurized by the double action, air actuated hydrostatic pump 127 and directed into the interior of the pressure vessel 91 through its base. Valve 129 controls the fiow of water into the vessel 91 and the Bourden type gauge 131 continuously registers the hydrostatic pressure of the system.

The water jacket structure 133 that surrounds the pressure vessel 91 is coupled to a suitable temperature controlled water supply source not shown in the drawing to control the ambient temperature of the electrolytic process within the permeation cell.

In operation, the specimen which is to be evaluated is secured in its holding device 9 between the electrolytic cells 37 and 57 of the apparatus 4. The cells 37 and 57 are then respectively filled with the above described sulfurichydrochloric acid and the sodium hydroxide-sodium chloride electrolytic solutions. Timpanic membranes 19 and 21 are then secured in position over the open ends of the cells. The permeation cell 4 is then suspended in the hydrostatic pressure cell 91 by snapping the male connectors of conductors 97-105 on the corresponding female connectors on the cell 4 and/ or by any other suitable suspension structure. The hydrostatic pressure and ambient temperature within the vessel 91 and the cell 4 are then adjusted to desired values and the external electrical circuitary 107 is connected to the conductors in the manner described hereinabove. By adjusting variable resistor 113, the potential across the cathodic cell 37 is controlled so as to provide a predetermined supply of hydrogen molecules on the upper surface of the specimen 3. Thus, when the potential is applied across cell 37, negative sulfate ions of the electrolyte migrate toward the positive anode and combine with disassociated ions of water to release electrons at the anode in accordance with the following equation:

Simultaneously, positive hydrogen ions of the electrolyte migrate toward the specimen cathode 3 and accept electrons to form hydrogen in accordance with the following equation:

A small percentage of atomic hydrogen never combines to form gaseous hydrogen. It is precisely this atomic hydrogen that diffuses through the metal lattice. By increasing and decreasing the potential across the cell 37, the supply of hydrogen on the cathodic surface of the specimen electrode 3 is correspondingly increased or decreased.

The electronic potentiostat 117 maintains a constant potential on the anodic surface of the specimen electrode 3 in the anodic cell 57. By monitoring the flow of current in the anodic cell 57 on the electrometer 121 and the recorder 123, a measure of hydrogen permeation through the specimen 3 is obtained. Thus, when a potential is applied across cell 57, positive sodium ions of the electrolyte migrate toward the negative cathode and combine with disassociated ions of the water accepting electrons at the cathode 55 in accordance with the following equation:

Simultaneously, the negative hydroxyl ions of the electrolyte migrate toward the specimen anode 3, combines with hydrogen that permeates through the specimen 3 and 4 releases electrons in accordance with the following equations:

H-e H+ H++OH- H O By varying the hydrostatic pressure as well as the temperature of the pressure vessel system, the predetermined controlled ambient pressures and temperatures are transmitted through the timpanic membranes 19 and 21 to the permeation cell 4. This is accomplished with accuracy in a scientifically clean electro-chemical process with the improved apparatus of the invention.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understod that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An apparatus for evaluating the electrochemical and diffustion parameters of hydrogen thru a metallic specimen, said apparatus comprising:

(a) wall means defining a hermetically sealed chamber, including means for transmitting ambient pressure changes to the inside of the chamber;

(b) means within said chamber for supporting said specimen to divide said chamber into first and second fluid isolated zones, having a first surface of said specimen facing the first zone and a second surface opposite said first surface facing the second zone;

(c) means including an inert anode positioned in said first zone for biasing said specimen cathodic relative to said anode and generating hydrogen in the presence of a suitable electrolyte at the surface of said specimen;

(d) means including an inert cathode positioned in the second zone for biasing the specimen anodic relative to said cathode electrolytically oxidizing hydrogen arriving at the second surface of said specimen by diffusion therethrough;

(e) means surrounding said chamber for subjecting said chamber to controlled changes in pressure;

(f) means in said first zone for monitoring voltage changes at the surface of said specimen during said changes in pressure;

(g) and means within said second zone for monitoring changes in current oxidizing hydrogen that permeates the specimen.

2. The apparatus substantially as described in claim 1 wherein the means for monitoring changes in current oxidizing hydrogen that permeates the specimen includes a potentiostat that maintains the specimen-anode of the second zone at a predetermined constant potential,

3. The apparatus substantially as described in claim 1 wherein the means for transmitting ambient pressure changes to the inside of the chamber includes a timpanic membrane.

4. The apparatus substantially as described in claim 1 wherein the means for subjecting the chamber to controlled changes in pressure is enclosed in a water jacket structure that controls the ambient temperature of the chamber.

References Cited UNITED STATES PATENTS 2,595,042 4/1952 Wyllie 20-195 2,882,212 4/1959 Beard 204- 2,886,497 5/1959 Butler 20'41.1X 2,930,967 3/1960 Laird et al 204-195X 3,296,113 1/1967 Hansen 204-195 3,325,378 6/1967 Greene et a1 204-195X JOHN H. MACK, Primary Examiner N. A. KAPLAN, Assistant Examiner U.S. Cl. X.R. 2041.1, 129 

